Enhanced Light Absorption and Photo‐Generated Charge Separation Efficiency for Boosting Photocatalytic H2 Evolution through TiO2 Quantum Dots with N‐Doping and Concomitant Oxygen Vacancy

Low-range light absorption and rapid recombination of photo-generated charge carriers have prevented the occurrence of effective and applicable photocatalysis for decades. Quantum dots (QDs) offer a solution due to their size-controlled photon properties and charge separation capabilities. Herein, well-dispersed interstitial nitrogen-doped TiO₂ QDs with stable oxygen vacancies (N-TiO_2-x-V_O) are fabricated by using a low-temperature, annealing-assisted hydrothermal method. Remarkably, electrostatic repulsion prevented aggregation arising from negative charges accumulated in situ on the surface of N-TiO_2-x-V_O, enabling complete solar spectrum utilization (200-800 nm) with a 2.5 eV bandgap. Enhanced UV-vis photocatalytic H₂ evolution rate (HER) reached 2757 µmol g^-1 h^-1, 41.6 times higher than commercial TiO₂ (66 µmol g^-1 h^-1). Strikingly, under visible light, HER rate was 189 µmol g^-1 h^-1. Experimental and simulated studies of mechanisms reveal that V_O can serve as an electron reservoir of photo-generated charge carriers on N-doped active sites, and consequently, enhance the separation rate of exciton pairs. Moreover, the negative free energy (-0.35 V) indicates more favorable thermodynamics for HER as compared with bulk TiO₂ (0.66 V). This research work paves a new way of developing efficient photocatalytic strategies of HER that are applicable in the sustainable carbon-zero energy supply.